a little reading and surfing led me to this page which I'll stick the link to below. It details the A/R , stoichiometry question , manifold types , and some other basics over four pages with little more than a paragraph on each . And it comes from a great authority on the topic too ! Garrett .
https://www.turbobygarrett.com/turbobygarrett/turbine_housing_AR_and_housing_sizing .

Ok so after reading this thread I do have a question. I have a 2006 Saab 9-3 2.0T and what this car can do is fantastic. I can go to a gas station, fill up with a full tank of 87 and the ECU automatically adjusts once that 87 hits the cylinders. Now here's my issue, and I hope someone is knowledgeable enough about Saabs to be able to answer this, is if I put a beefier turbo on my car according to the OP I would have to adjust the fuel flow to match. Is this going to be true with how my cars ECU works? In other words do you guys think that the car will see the extra boost and be able to adjust the fuel flow itself? Because if not then I have two options.

First, spend another $1200-$1500 to get a fully programmable ECU complete with software and data cable shipped from someplace in Europe and hope to God whoever translated the manual speaks fluent English.

Second, spend $400 total on two things from two completely different sellers for something called a Tech2 and the data cable and then search for the software to use the Tech2 which GM hates sharing and hope that wherever I find it also included instructions.

I am new to turbos and I have a 2009 4.0 v6 mustang 2 mods away from full bolt ons and I already have a tuner with life time tunes. I was hoping someone can help me out with one question so I am looking for a t3 / t4 hybrid v band ball bearing 60mm turbo oil cooled I just don't know if turbos are a universal set up where I can buy the turbo and mount it any where or are they prapiatery to mounting.

I am new to turbos and I have a 2009 4.0 v6 mustang 2 mods away from full bolt ons and I already have a tuner with life time tunes. I was hoping someone can help me out with one question so I am looking for a t3 / t4 hybrid v band ball bearing 60mm turbo oil cooled I just don't know if turbos are a universal set up where I can buy the turbo and mount it any where or are they prapiatery to mounting.

T3/T4 hybrids put the turbine from a small turbo onto the compressor for a large one. The goal with this design is to feed a very high amount of boost to a small engine that would not be able to spin the compressor up with the original T4 turbine. This is the wrong turbo to use on a 4.0 V6 unless you want 25 psi of boost... and want to run two of them. A turbo needs to be sized to match the engine. They're not one size fits all.